A thermal transfer recording system using a thermal head has come to be used for various uses such as label printers, ticket delivering machines and word processors. As these uses are expanded, printed matters have come to be used in a severer environment than in conventional ones.
Further, as printed matters are used in a severer circumstance, media to be transferred have been expanded in use from conventional paper to plastic films having less dependency on the environment. For example, there have been caused the problems that when such special media as a plastic film into which a thermal transfer ink can not penetrate are used for a medium to be transferred, ribbons containing conventional thermal transfer ink compositions mainly comprising waxes can not provide good transfer, or though images are transferred, the transferred images are removed by simple abrasion, and thus the required mechanical abrasion resistance can not be satisfied.
Further, a great variety of thermal heads is used for printers, and a speed-up in the printing speeds and an increase in the dot densities are intended, so that a heavy load is put on thermal transfer media used. Accordingly, thermal transfer media having more excellent transfer performance have been desired.
There have so far been known examples in which special resins or components are used in a thermal transfer ink layer to try to solve the problems described above. Thermal transfer recording materials containing colorants and specific kinds of resins limited in various conditions are disclosed in Japanese Patent Application Laid-Open No. Sho 62-13384, and as is the case with Japanese Patent Application Laid-Open No. Sho 63-230392, proposed are thermal transfer recording materials comprising a specific amount of each of colorants, specific kinds of resins limited in a glass transition point and lubricants.
They are intended to satisfy the transfer performance and the durability of the printed matters by virtue of the constitutions thereof. These proposals have provided the good transfer performance to some extent and the durability of the printed matters to some extent but have not been able to provide such sufficient effects as required in the present invention.
As described above, matters printed by thermal transfer printing by means of thermal heads have come to be used in a severer environment than in conventional ones. Such are, for example, use at severe room temperature, mechanical abrasion of printed matters, contact with solvents and use under an environment of exposing outdoors.
Such circumstances have resulted in using special durable media for media to be transferred as described above and have brought about problems on good transfer onto a plastic film and on obtaining printed matters having required durability.
That is, a large problem has been caused on compatibility of capability of good thermal transfer onto a durable medium to be transferred such as a plastic film with obtaining printed matters having sufficiently high mechanical abrasion resistance, solvent resistance against various solvents and light fastness against rays such as UV rays, and it has been considered that a large key for solving the problem described above resides in the components of a thermal transfer ink layer of a thermal transfer recording medium, a so-called ink ribbon. The compositions of thermal transfer ink layer components have so far been investigated, but proposals satisfying the standards required in the present invention have not yet been made. An object of the present invention is just to propose means for solving the problem described above.